1. Field of the Invention
The present invention generally relates to a communication system, and more particularly to a duobinary voltage-mode (VM) transmitter.
2. Description of Related Art
FIG. 1 shows a block diagram of a wireline communication system 100 for transmitting and receiving data. Data are converted to a serial data stream by a serializer (SER) 11 to facilitate transmission over a single or a pair of differential lines. Transmit equalization is performed by a finite-impulse-response (FIR) filter 12, followed by a driver 13. Data are transmitted over a channel 14 such as a single or a pair of differential lines, and is received and processed by an equalizer (EQ) 15 to reduce intersymbol interference (ISI). The received data stream is then processed by a clock and data recovery (CDR) 16, followed by a deserializer (DES) 17 which converts the data stream into a parallel data format.
Power consumption and impedance match are two of crucial issues in designing a transmitter of a wireline communication system 100. “Digital Link Pre-emphasis with Dynamic Driver Impedance Modulation,” entitled to Ranko Sredojevic et al., IEEE ISSCC 2010, the disclosure of which is incorporated herein by reference, discloses a digital push-pull impedance-modulating (RM) pre-emphasis driver to overcome the power overhead of equalization in voltage-mode (VM) drivers, improving the output stage efficiency. In the disclosure, differential path with impedance is shorted when data pattern is “11111 . . . ” or “00000 . . . ” There is no short circuit current, and consumed power is almost the same. However, there is still some room to improve regarding power consumption.
“Fully Digital Transmit Equalizer With Dynamic Impedance Modulation,” entitled to Ranko Sredojevic et al., IEEE JSSC 2011, the disclosure of which is incorporated herein by reference, discloses a digital push-pull impedance-modulating (RM) driver. In the disclosure, impedance is increased to reduce the power consumption when data pattern is “11111 . . . ” or “00000 . . . ” According to the disclosure, voltage-mode (VM) power is different for different output voltage, however, with bad impedance match.
For the reason that conventional transmitters could not effectively reduce power consumption and improve impedance match, a need has arisen to propose a novel transmitter to overcome disadvantages of the conventional transmitters.